Adding to what @viswaram pointed currently, exchange offering cross margin benefit is not straight forward operationally since broker has to upload the files with necessary details. Also, even if broker wants to offer this facility, they need to full fill the below mentioned clearing and settlement criteria and the current criteria’s doesn’t look easy as we speak.
Apart from operational complexity, few points:
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The spread benefit is only passed for Futures and not for Options. Also, portfolio with hedge benefit or calendar spread will not get cross margin benefit as the portfolio is already covered for risk.
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Portfolio should be exact replica that means no. of shares in the holdings should be equal to the lot size and no partial benefit.
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No clarity on corporate actions like Bonus issue, merger which impact F&O lot size. Because Bonus shares or merged entity (if not listed) will come much later than the F&O lot size impact on ex-date. Also, no clarity on F&O having periodical review (every 6 months once) of lot size whenever contract size increase/drops beyond the exchange stipulated criteria.
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In case of Physical delivery, you will have give delivery position (short against holdings) and failed to sqroff or roll over would debit your shares towards to the obligation. Again no clarity on how the delivery margin, etc. are applicable since Peak, physical delivery are introduced in last 3-4 yrs compare to cross margin feature.
There will be some more points which I might have missed. Having said that, we appreciate your feedback 
and may give a try in future.